linux-kernel - RE: [git head] Should X86_PAT really default to yes?

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Date:	Fri, 2 May 2008 12:37:32 -0700
From:	"Pallipadi, Venkatesh" <venkatesh.pallipadi@...el.com>
To:	"Frans Pop" <elendil@...net.nl>, <linux-kernel@...r.kernel.org>
Cc:	"Ingo Molnar" <mingo@...e.hu>,
	"Barnes, Jesse" <jesse.barnes@...el.com>,
	"Packard, Keith" <keith.packard@...el.com>
Subject: RE: [git head] Should X86_PAT really default to yes?

 

>-----Original Message-----
>From: Frans Pop [mailto:elendil@...net.nl] 
>Sent: Friday, May 02, 2008 12:22 PM
>To: linux-kernel@...r.kernel.org
>Cc: Pallipadi, Venkatesh; Ingo Molnar
>Subject: [git head] Should X86_PAT really default to yes?
>
>With X86_PAT enabled, when X is started I get about 40 lines 
>(with varying 
>addresses) like:
>kernel: Xorg:3358 /dev/mem expected mapping type write-back for 
>807bf000-81000000, got uncached-minus
>
>And when X exits I get a bunch of lines like:
>kernel: Xorg:3349 freeing invalid memtype 80020000-8002a000
>
>I also noticed artifacts (a band of about 2 cm high across the 
>screen) after 
>X goes to black but before the switch to VT1.
>
>When I unset X86_PAT all this disappeared.
>
>Apparently this has been seen before:
>http://lkml.org/lkml/2008/5/2/139
>
>The author of that mail also points to:
>http://marc.info/?l=linux-kernel&m=120612742217604&w=2
>
>Is this a bug in PAT or not. If it is, should PAT really be 
>recommended to 
>be enabled by default?
>
>System: Intel desktop with D945GCZ mainboard
>        Intel(R) Pentium(R) D CPU 3.20GHz
>        x86_64 kernel; Debian unstable
>Video:  00:02.0 VGA compatible controller [0300]:
>        Intel Corporation 82945G/GZ Integrated Graphics Controller
>        [8086:2772] (rev 02)
>

Copying the X-guys.
The messages all look like debug messages from X and should not cause
any side-effects other than little annoyance. I am not sure why band of
2 cm is there...
Do you see any performance difference with or without PAT.

Thanks,
Venki
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